package pf.java.pfHelperBackup;

import java.io.*;  

/**
 * 为解决读UTF-8文件第一个字符的BUG.功能相当于原本的InputStreamReader
 * @author Benjamin
 *
 */
public class UnicodeReader extends Reader {  
  PushbackInputStream internalIn;  
  InputStreamReader   internalIn2 = null;  
  String              defaultEnc;  
  
  private static final int BOM_SIZE = 4;  
  
    
  public UnicodeReader(InputStream in, String defaultEnc) {  
     internalIn = new PushbackInputStream(in, BOM_SIZE);  
     this.defaultEnc = defaultEnc;  
  }  
  
  public String getDefaultEncoding() {  
     return defaultEnc;  
  }  
  
    
  public String getEncoding() {  
     if (internalIn2 == null) return null;  
     return internalIn2.getEncoding();  
  }  
  
    
  protected void init() throws IOException {  
     if (internalIn2 != null) return;  
  
     String encoding;  
     byte bom[] = new byte[BOM_SIZE];  
     int n, unread;  
     n = internalIn.read(bom, 0, bom.length);  
  
     if ( (bom[0] == (byte)0x00) && (bom[1] == (byte)0x00) &&  
                 (bom[2] == (byte)0xFE) && (bom[3] == (byte)0xFF) ) {  
        encoding = "UTF-32BE";  
        unread = n - 4;  
     } else if ( (bom[0] == (byte)0xFF) && (bom[1] == (byte)0xFE) &&  
                 (bom[2] == (byte)0x00) && (bom[3] == (byte)0x00) ) {  
        encoding = "UTF-32LE";  
        unread = n - 4;  
     } else if (  (bom[0] == (byte)0xEF) && (bom[1] == (byte)0xBB) &&  
           (bom[2] == (byte)0xBF) ) {  
        encoding = "UTF-8";  
        unread = n - 3;  
     } else if ( (bom[0] == (byte)0xFE) && (bom[1] == (byte)0xFF) ) {  
        encoding = "UTF-16BE";  
        unread = n - 2;  
     } else if ( (bom[0] == (byte)0xFF) && (bom[1] == (byte)0xFE) ) {  
        encoding = "UTF-16LE";  
        unread = n - 2;  
     } else {  
        // Unicode BOM mark not found, unread all bytes  
        encoding = defaultEnc;  
        unread = n;  
     }      
     //System.out.println("read=" + n + ", unread=" + unread);  
  
     if (unread > 0) internalIn.unread(bom, (n - unread), unread);  
  
     // Use given encoding  
     if (encoding == null) {  
        internalIn2 = new InputStreamReader(internalIn);  
     } else {  
        internalIn2 = new InputStreamReader(internalIn, encoding);  
     }  
  }  
  
  public void close() throws IOException {  
     init();  
     internalIn2.close();  
  }  
  
  public int read(char[] cbuf, int off, int len) throws IOException {  
     init();  
     return internalIn2.read(cbuf, off, len);  
  }  
  
}  